Combination amplitude-modulationfrequency-modulation receiver



y 1941. .1. F. FARRINGQTON 2,250,862

COMBINAT ION AMPLITUDE-MODULATION- FREQUENGY-MODULAT I ON RECEIVER FiledJuly 16, 1940 V AL I0 vvvv INVENTOR J HN F. FARRINGTON ATTORNEY PatentedJuly 29, 1941 COMBINATION ANNE-MODULATION- FBEQUENCY-MODULATION RECEIVERJohn F..Farrington, wom n. 11., minor to Hazeltine Corporation, acorporation of Delaware .11 Claims.

' This invention relates generally to modulated- Application July 16,1940, Serial No. 345,726

carrier signal receivers for receiving and repro-- ducing bothamplitude-modulated and frequen- -cy-modulated carrier signals and.particularly,

to such a receiver in which a single carrier-' frequencysignal-translatingstage is utilized as a limiter when receiving afrequency-modulated signal and as an amplitude-modulation detector whenreceiving an amplitude-modulated signal.

Certain units of a modulated-carrier wave-signal receiver for receivingan amplitude-modulated signal are identical with, or very similar to,corresponding unitsof a receiver for receiving and reproducinga-frequency-modulated carrier signal. It has previously been proposed tousecertain of suchunits as common elementsin a combinedamplitude-modulation and frequency-modulation receiver. However, thecircuits which have heretofore been used are somewhat more complicatedor less satisfactory in operation than is desired. Certainreceivers forreceiving a frequency-modulated carrier wave require a separate stage inthe signal-translating channel of the receiver, the function of which isto limit the translated signal to eliminate therefrom anyamplitude-modulation components and amplitude variations. However, ifparts ofa frequency-modulation receiver circuit are to'be used also inthe circuit of an amplitude-modulation receiver in which alimitingaction is not,

as an amplitude limiter over a given carrier-.

1 wave corresponding to a signal within the given tolerable, the limiterstage of the frequencymodulation receiver is generally used simply'as acarrier-frequency amplifier in the circuit of the amplitude-modulationreceiver. However. sufficient carrier-frequency amplification for allpurposes must also be provided for the frequencymodulation receivercircuit so that the additional amplification provided by using thelimiter stage as an amplifier in the circuit of the amplitudemodulationreceiver really serves no useful purpose. Furthermore, a different typeof detector circuit is required in a frequency-modulation receiver thanin an amplitude-modulation receiver. Therefore, it is very desirable tobe able to use the limiter stageof a frequency-modulation receiver as anamplitude detector in an amplitude-modulation receiver.

It is an object of the invention, therefore, to providean improvedreceiver circuit for receiving either an amplitude-modulated carrierwave or a frequency-modulated carrier wave in which one ormore -of theabove-mentioned disadvantages of prior art circuits are eliminated.

I It is still anotherobject of the invention to provide a combinationamplitude-modulation- 551i and 32, respectively, to either thefrequencyfrequency modulation receiver in which a singlecarrier-frequency signal-translating stage serves as a limiter when theapparatus is being utilized to receive a frequency-modulated carriersignal and as an amplitude detector when the apparatus is being utilizedto receive an amplitudemodulated signal.

In accordance with the invention, a modulatedcarrier wave-signalreceiver comprises a carrierirequency signal-translating stage and meansincluded in the stage for causing the stage to act frequency range, sothat amplitude modulation is removed from translated signals within'thegiven carrier-frequency range. Means are also included in the stage forcausing the stage to act as 'an amplitude-modulation detector over theabove-mentioned carrier-frequency range. a

Means are further provided for selectively utilizing a first signaloutput from the stage to reproduce a received frequency-modulatedcarrier frequency range or a second signal output from the stage toreproduce a received amplitudemodulated carrier wave corresponding to asignal within the given frequency range. For a better understanding. of'the invention,

together with other and further objects thereof,

reference is had to the following description taken in connection withthe accompanying drawing, and its scope will be pointed out in theappended claims;

The single figure of the drawing represents a modulated-carrierwave-signal receiver of the superheterodyne type for receiving either anamplitude-i'nodulated carrier signal are. frequency ing, the systemillustrated comprises a receiver modulated carrier signal.

Referring now more particularly to the drawof the superheterodyne typeincluding an antenna circuit H), II connected to a radio-frequencyamplifier l 2 to which are connected in cascade, in the order named, anoscillator-modulator l3, an intermediate-frequency amplifier l4, and acarrier-frequency signal-translating stage 15 which acts as a limiterwhen frequency-modulated carrier signals are being received and whichacts as an amplitude-modulation detector when amplitude-modulatedcarrier signals are being received. A frequency-modulation detector I6is coupled to one output circuit of carrier-frequency signal-translatingstage l5, while an audio-frequency amplifier ll is selectivelyconnected, by means 101 a switch It and coupling condensers modulationdetector I. or to an output circuit of carrier-frequencysignal-translating stage II for receiving detected amplitude-modulationcomponents of adesired received signal. A signal-reproducing device I.is coupled to the output circuit of audio-frequency amplifier II. Itwill be understood that frequency-modulation detector I. may be of aconventional type and, as shown, is of the type comprising a transformerhaving a primary winding 20,'tuned to the mean frequency of theintermediate-frequency channel of the receiver by a condenser 2|, and asecondary winding 22, also tuned to the mean frequency of theintermediate-frequency channel of the receiver by a condenser 23.Damping is provided in the tuned primary winding of transformer 20, 22by means of a resistor 20'. Diodes 24, 25 are provided having loadcircuits therefor including resistors 26 and 21, by-passed forcarrier-frequency currents by a condenser 28. In order to supply avoltage proportional to the vector sum of the voltages of the primaryand secondary windings of transformers 2|, 22 to one of the diodes andto provide a voltage proportional to the vector difierence of thevoltagm of the primary and secondary windings to the other of thediodes, a coupling condenser 29 is coupled between one side i of winding20 and a mid-tap on winding 22, while the mid-tap of winding 22 iscoupled to the com mon junction of resistors 26 and 21'. Automaticfrequency control potentials are derived from frequency detector I 6 andapplied by means of the conductor designated AFC -to an automaticfrequency control unit 30 which is coupled to oscillator-modulator I3 tocontrol the frequency of the oscillator section thereof in a manner wellunderstood in the art.

The stages or units I to I4, It to I8 and 30 may all be of conventionalwell-known construction so that detailed illustration and descriptionthereof are deemed unnecessary herein. Refer ring briefiy, however, tothe operation of the system described above, a desired received carriersignal, which may be either frequency-modulated or amplitude-modulated,is intercepted by antenna circuit III, II and is selected and amplifledin radio-frequency amplifier I2 and coupled to the oscillator-modulatorI3 wherein it is converted into an intermediate-frequency signal which,in turn, is selectively amplified in the intermediate-frequencyamplifier I 4 and coupled to the carrier-frequency signal-translatingstage I5. If the desired received signal is a frequencymodulated carriersignal, the switch I9 is thrown so that audio-frequency amplifier I1 isconnected to an output circuit of frequency-modulation detector I6. Thedesired intermediate-frequency signals are, therefore, limited incarrier-frequency signal-translating stage I5 and detected infrequency-modulation detector I6, the detected components thereof beingsupplied through audiofrequency amplifier I! to signal reproducer I8 forreproduction.

If the desired received signal is an amplitudemodulated carrier signal,the switch I9 is thrown so that audio-frequency amplifier I1 is coupledto carrier-frequency signal-translating stage I5 in order to supply toaudio-frequency amplifier I I the desired amplitude-modulationcomponents for reproduction.

In either case a voltage varying in accordance with the degree ofmistuning of the receiver is derived from unit I 6 and applied to-t'heautomatic frequency control unit 30 over the conductor labeled A. F. C.to control the tuning of the receiver in a manner which is, per so, wellunderstood by those skilled in the art.

Coming now to the portion of the system embodylng an essential featureof the present invention, there is included in the carrier-frequencysignal-translating stage I5 a vacuum tube 35, the circuit of whichincludes means for causing the stage to act as an amplitude limiter overa given carrier-frequency range so that amplitude modulation is removedfrom translated signals within a given carrier-frequency range. Meansare also included for causing the stage to act as anamplitude-modulation detector over the given carrier-frequency range. Tothis end, input circuit of vacuum tube 35 includes a parallel-resonantcircuit comprising an inductance 36 inductively coupled to an inductance31 which is, in turn, coupled to the output terminals ofintermediate-frequency amplifier II. The secondary winding 38 of thetransformer 31, 38 is tuned to the intermediate-carrier frequency of thereceiver by means of a condenser 38, the tuned circuit being damped by aresistor 36'.

In order to cause the input circuit of tube 35 to act as anamplitude-modulation detector, there is provided in series with tunedcircuit 36, 38 a suitable load circuit including a resistor 39 and aresistor 40 by-passed for carrier-frequency currents by condensers IIand 42. The output circuit of tube 35 comprises tuned circuit 20, 2| offrequency-modulation detector I6. The unidirectional voltage developedacross resistor III is applied through a suitable audio-frequencyfilter, including a series resistor 43 and a shunt condenser and theconductor labeled AVC, to one or more tubes of radio-frequency amplifierI2, the oscillator-modulator II, and intermediatefrequency amplifier IIto maintain the amplitude of the signal input to stage I5 within arelatively narrow range for a wide range of received signal amplitudes.Resistor 39 and condenser 42 are proportioned to have a suitabletime-constant and the screen grid of tube 35 is maintained at arelatively low potential so that a quickly-responsive limiting action iseffected in signals translated to the anode circuit of tube 35.

In considering the operation of the portion of the circuit Justdescribed, it will be seen that resistor 40 forms a suitable loadcircuit so that amplitude-modulation components of the received carriersignal are detected in the input circuit of tube 35. Specifically theinput circuit of tube" acts as a diode detector, theintermediate-frequency signals of the receiver being applied theretothrough tuned circuit 36, 38 and amplitude-modulation components of thesignal being derived across resistor 40. Elements 3! and ll effectivelycomprise a carrier-frequency filter which aids in eliminatingcarrier-frequency signals from the output to condenser I2 or to the AVGcircuit. Therefore, switch I9 is included in a means for selectivelyutilizing a first signal output from stage I5, derived throughfrequencymodulation detector I 6, to reproduce a receivedfrequency-modulated carrier wave corresponding to a signal within agiven frequency range, or for utilizing a second signal output from thestage, derived from load circuit 40, II, to reproduce a receivedamplitude-modulated carrier signal corresponding to a signal within thegiven frequency range. When operating as a frequency-modulation receiverthe elements I9, 42 efiectively comprise a fast time-constant circuit sothat the grid of tubeIll,,-ln addition to the usual limiting actionthereo provided by thetime-constant circuit in r cluding elements to, 4l is made substantially less responsive to higher-frequency componentssuch as noise components. 7

While it is not intended to limit the circuit of the invention to anyparticular circuit values,

there follows a list of circuit values whicli'have been found to beparticularly efiective in the circuit of Fig. 1. a

Tube as Type 6831 Condenser 4| 400 micro-microfarads Condenser 42 50micro-microfarads Condenser l4 0.02 microfarad I Resistor 38 50kilohms.Resistor 40---. 250 kilohms Resistor l3 1 megohm Resistor 36' lrilohmsResistor 20' 20 kilohms Tuned circuits 36-38, 20,

2|,and 22, 23 Tuned to a frequency of 2900 kilocycle's I While there hasbeen described what is at present considered to be the preferredembodiment of this invention, it will be obvious to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the invention, and it is, therefore, aimed in theappended claims to cover all such changes and amplitude modulation isremoved from translated signals-within said given carrier-frequencyrange, means for detecting amplitude-modulation components in said inputcircuit and for deriving a signal output therefrom, and means forselectively utilizing a signal output from said output circuit toreproduce a received frequency-modulated carrier wave corresponding to asignal within said given frequency range or said detectedamplitude-modulation components to reproduce a receivedamplitude-modulated carrier wave corresponding to a signal within saidgiven fre-' quency range.

4. A modulated-carrier wave-signal receiver comprising, acarrier-frequency signal-translating stage including a vacuum tubehaving input and output circuits, means included in said stage forvcausing said stage to act as anamplitude limiter over a givencarrier-frequency range so that amplitude modulation is removed fromtranslated signals within said given carrier-ire quency range,- meanscomprising a tuned'circuit and a time-constant circuitin said inputcircuit for detecting amplitude-modulation components and for deriving asignal output therefrom, and

modifications as fall within the true spirit and;

scope of the invention.

What is claimed is:

1. A- modulated-carrier wave-signal receiver comprising, acarrier-frequency signal-translating stage, means included in said stagefor causing said stage to act as an amplitude limiter over a givencarrier-frequency range so that amplitude 'modulation is removed fromtranslated signals within said given carrier-frequency range, meansincluded in said stage for causing said stage to' act as anamplitude-modulation detector over.

said given carrier-frequency range, and means a given carrier-frequencyrange so that amplitude modulation is removed from translated sigmeansfor selectively utilizing a signal output from said output circuittoreproduce a received frequency-modulated carrier wave corresponding to asignal within said given frequency range, or said detectedamplitude-modulation components to reproduce a receivedamplitude-modulated carrier wave corresponding to a signal within saidgiven frequency range.

5. A modulated-carrier wave-signal .receiver comprising, acarrier-frequency signal-translat- ,ing stage'including a vacuum tubehaving input and output circuits, means including a tuned circuit and atime-c'onstant circuit for'causing said stage to, act as an amplitudelimiter over nals within said carrier-frequency range, means includedin-said stage for'causlng said stage to act as an amplitude detectorover said givencar- '-rier-frequency range, andmeans for selectivelyutilizing a first signal output from. said stage 'to reproduce areceived frequency-modulated carrier wave corresponding to a signalwithin said .given frequency range, or amplitude-modulationcomponentsderived from said stage to reproduce and output circuits,means included in said stage for causing said stage to'act as anamplitude limiter over a given carrier-frequency range so that amplitudemodulation is removed from translated signals within said givencarrier-frequency range, means included in said stage for causing saidstage to act as an amplitude-modulation detector over said givencarrier-frequency range, and means for selectively utilizing a signaloutput from said output circuit to reproduce a receivedfrequency-modulated carrier wave corresponding to a signal within saidgiven frequency range, or

a signal output fromsaid input circuit to reproduce a receivedamplitude-modulated carrier wave corresponding to a signal within saidgiven frequency range.

3. A modulated-carrier wave-signal. receiver comprising, acarrier-frequency signal-translating stage including a vacuum tubehaving input a received amplitude-modulated 'carrier wave correspondingto a signal within said. given fre- I quen'cy range.

6. A modulated-carrier wave-signal receiver comprising, acarrier-frequency signal-translating stage including a vacuum tubehaving input and output circuits, means including is. tuned circuit-anda time-constant circuit in said input circuit for causing said stage toact as an amplitude limiter over a given carrier-frequency range so thatamplitude modulation is removed from translated signals within saidgiven carrier frequency range, means included in said stage andincluding said tuned circuit and said timeconstant circuit for causingsaid stage to act as an amplitude detector over said given carrier- Ifrequency range,and means for selectively utilizing aflrst signal outputfrom said stage to reproduce a received frequency-modulated carrier wavecorresponding to a signal within said given 7 frequencyrange, or theamplitude-modulation components developed in said time-constant cirandoutput circuits, means included in said stage cuit to reproduce areceived amplitude-modufor causing saidstage to-act as an amplitudeJim-'- iter over a given carrier-frequency range so that lated carrierwave corresponding to a signal within said given frequency range.

, 7. A modulated-carrier wave-signal receiver comprising, acarrier-frequency signal-translat-' ing stage including a vacuumtubehaving input and output circuits, means including a tuned circuit and atime-constant circuit in said input circuit for causing said stage toact as an amplitude limiter over a given carrier-frequency range so thatamplitude modulation is removed from translated signals within saidgiven carrier-frequency range, means included in said stage andincluding said tuned circuit and said time-constant circuitfor causingsaid stage to act as an amplitude detector over said givencarrier-frequency range, means ior selectively utilizing a first signaloutput from said stage to reproduce a received frequency-modulatedcarrier wavesponsive to higher-frequency modulation components when thereceiver is acting. as a frequency-modulation receiver.

8. A modulated-carrier wave-signal receiver comprising, acarrier-frequency signal-translating stage including a vacuum tubehaving an input circuit and an'output circuit, means included in saidstage for causing said stage to act as an amplitude limiter over a givencarrier-frequency range so that amplitude modulation is removed fromtranslated signals within said given carrierirequency range, meansincluded in said stage for causing said stage to act as anamplitude-modulation detector over said given carrier-frequency range,means included in said input circuit for deriving an automaticamplification control voltage for said receiver, and means forselectively utilizing a first signal output from said stage to reproducea received frequency-modulated carrier wave corresponding to a signalwithin said given frequency range, or a second signal output from saidstage to reproduce a received amplitudemodulated carrier wavecorresponding to a signal within said given frequency range.

9. A modulated-carrier wave-signal receiver comprising, acarrier-frequency signal-translating stage, a frequency-modulationdetector coupled to said stage, means included in said stage for causingsaid stage to act as an amplitude limiter over a. givencarrier-frequency range so that amplitude modulation is removed fromtranslated signals within said given carrier-frequency range, meansincluded in said stage for causing said stage to act as anamplitude-modulation detector over said given carrier-frequency range,and means for selectively utilizing a first signal output derived fromsaid stage through said frequency-modulation detector to reproduce areceived frequency-modulated carrier wave cor-. responding to a signalwithin said given frequency range, or a second signal output from saidstage to reproduce a received amplitude-modulated carrier wavecorresponding to a signal within said given frequency range.

10. A modulated-carrier wave-signal receiver comprising, acarrier-frequency signal-translating stage, a frequency-modulationdetector coupled to said stage, means included in said stage for causingsaid stage to act 'as an amplitude limiter over a givencarrier-frequency range so that amplitude modulation is removed fromtranslated signals within said given carrier-irequency range, meansincluded in said stage for causing said stage to' act as anamplitude-modulation detector over said given carrier-frequency range,means for deriving a voltage from said frequency-modulation detector toprovide an automatic-frequency control for said receiver, and means forselectively utilizing a first signal output derived from said stagethrough said frequency-modulation detector to reproduce a receivedfrequency-modulated carrier wave corresponding to a signal within saidgiven frequency range, or a second signal output from said stage toreproduce a received amplitude-modulated carrier wave corresponding to asignal within said given frequency range.

11. A modulated-carrier wave-signal receiver comprising, acarrier-frequency signal-translating stage, means included in said stagefor causing said stage to act as an amplitude limiter over a givencarrier-frequency range so that amplitude modulation is removed fromtranslated signals within said given carrier-frequency range, meansincluded in said stage for causing said stage to act as anamplitude-modulation detector over said given carrier-frequency range, asignal reproducer, and means for selectively deriving a first signaloutput from said stage and applying it to said signal reproduced toreproduce a received frequency-modulated carrier wave corresponding to asignal within said given frequency range, or a second signal output fromsaid stage and applying it to said signal reproducer to reproduce areceived amplitude-modulated carrier wave corresponding to a signalwithin said given frequency range, said last-named means comprisingmeans for disconnecting the circuit for translating each of said signaloutputs to said signalreproducer during the time when the other of saidsignal outputs is being supplied to said signalreproducer.

JOHN F. FARRINGTON.

